1. Field of the Invention
The present invention relates to a webbing take-up device for a seat belt apparatus for restraining a vehicle occupant by means of a webbing belt.
2. Description of the Related Art
In a webbing take-up device, which is a principal portion of a seat belt apparatus which restrains a vehicle occupant by means of an elongated belt-shaped webbing belt, there is provided a take-up shaft to which one longitudinal direction end portion of the webbing belt is anchored. The take-up shaft is urged by an urging means such as a spiral coil spring in a direction in which the webbing belt is taken up. When the webbing belt which has been taken up on the take-up shaft is pulled out, the urging force from the urging means acts on the webbing belt. The urging force works as a restraining force which restrains the body of a vehicle occupant in the state in which the webbing belt is applied to the vehicle occupant.
The take-up shaft is supported either directly by a pair of leg plates which are formed at a frame, or indirectly via supporting members which are provided at the leg plates. Each of the leg plates is usually formed in a plate shape. In the case where the leg plates support the take-up shaft directly, the take-up shaft is supported by the leg plates in a manner in which the take-up shaft penetrates the leg plates at supporting holes or the like which are formed at the transverse direction central portion of the leg plates. On the other hand, in the case where the leg plates support the take-up shaft indirectly, the take-up shaft is supported by the leg plates in a manner in which the take-up shaft penetrates through through-holes which are formed at the transverse direction central portion of the leg plates, and is supported by supporting members attached to the leg plates.
One transverse direction end portion of each leg plate is integrally connected to a transverse end portion of a plate-shaped connecting portion. The webbing take-up device is mounted to a vehicle by fixing a portion of the connecting portion to a predetermined region of the vehicle by a fastening means such as a bolt.
When considering the fuel consumption and the like of a vehicle, it is preferable that the structural components of a webbing take-up device be as light as possible. One means for lightening the structural components of a webbing take-up device is lightening the aforementioned frame. Since the connecting portion of the frame is in a plate shape as described above, lightening of the frame can be readily attained by engraving the connecting portion to form appropriate holes or thinned portions.
On the other hand, when the webbing belt is pulled out, tensile force is applied to the connecting portion via the take-up shaft, the leg plates and the like. While the take-up shaft is provided corresponding to the transverse direction central portions of the leg plates as described above, the connecting portion is provided at respective ones of the transverse direction ends of the leg plates. Thus, when the webbing belt is pulled out, a torque about the portion of the connecting portion that is fixed to the vehicle is generated, which will deform the connecting portion in the direction of the torque. From the viewpoint of ensuring and maintaining the restraining force of the webbing belt, it is preferable that the connecting portion deforms as little as possible when acted on by the aforementioned tensile force.
However, random engraving of the connecting portion in order to lighten the same will considerably lower the rigidity of the connecting portion with respect to the aforementioned tensile force, and the connecting portion will be elastically deformed in the direction of the torque when acted on by the aforementioned tensile force.
In view of the aforementioned, an object of the present invention is to provide a webbing take-up device equipped with a frame which ensures sufficient rigidity and is light-weight.
A first aspect of the present invention is a webbing take-up device for taking-up and unwinding a webbing belt in a vehicle, the webbing belt having an end, wherein the belt is for fastening around a vehicle occupant, the device comprising a rotatably mounted take-up shaft adapted for receiving and anchoring an end of the webbing belt, and rotatably urged in a direction for taking-up the webbing belt and a frame having a pair of leg plates opposing each other between which the take-up shaft extends, a connecting portion integrally extending from one leg plate to the other, and a fixing portion adapted for fastening to the vehicle, the connecting portion having a plurality of apertures defined therein, at least some of the apertures formed as an elongated hole having a longitudinal axis formed substantially along a direction in which tensile force is applied via the take-up shaft and leg plates when the webbing belt is unwound.
In the webbing take-up device which is structured as described above, the take-up shaft, which is supported directly or indirectly by the leg plates of the frame, is urged in the direction in which the webbing belt, whose one end portion is engaged with the take-up shaft, is taken up. When a webbing belt which has been pulled out from the take-up shaft is applied to a vehicle occupant, the body of the vehicle occupant is restrained by the webbing belt which is urged by the urging force in the direction in which the webbing belt is taken up.
In the present webbing take-up device, because engraved portions formed by holes or thinned portions are formed in the connecting portion which connects the pair of leg plates, the connecting portion is lightened by the weight which has been removed by thinning or by the weight corresponding to the volume of the holes.
The engraved portions are formed along the direction in which tensile force acts on the connecting portion via the leg plates when the webbing belt which is taken up on the take-up shaft is pulled out, in the state in which the fixing portion of the connecting portion is fixed to the vehicle body. Furthermore, there are a plurality of engraved portions and these engraved portions are formed parallel to each other along the direction in which the tensile force acts. Therefore, between the engraved portions, there are formed portions that are not thinned portions or holes, whose longitudinal direction is along the direction in which the tensile force acts and whose widths are constant. As a result, the elasticity of the connecting portion against the tensile force is made uniform as compared to a case in which the engraved portions are randomly formed in the connecting portion.
The webbing take-up device of the present invention preferably includes the engraved portions formed continuously or intermittently along the direction from the fixing portion toward the pivotal portions which pivotably support the take-up shaft.
In the webbing take-up device which is structured as described above, the engraved portions are continuously or intermittently formed along the direction from the fixing portion of the connecting portion (that is, the portion at which the frame is fixed to the vehicle body), toward the supporting portion of the take-up shaft. In other words, the tensile force that acts on the take-up shaft when the webbing belt is pulled out acts on the support portions that pivotably support the take-up shaft. On the other hand, since the frame is fixed to the vehicle body at the fixing portion of the connecting portion, the connecting portion resists the tensile force at the fixing portion. Thus, the direction in which the tensile force acts on the connecting portion of the frame is the same as the direction from the fixing portion toward the supporting portion of the take-up shaft. The elasticity of the connecting portion with respect to the tensile force can be made even more uniform by forming the engraved portions continuously or intermittently along this direction, and by forming the regions between the engraved portions to have constant widths and such that the longitudinal directions thereof are along the direction of the tensile force.
The webbing take-up device of the present invention is preferably includes a locking device which locks prevents said take-up shaft from rotating in a direction for unwinding when the vehicle is in a state of rapid deceleration, the locking device including a connective part connecting said take-up shaft to at least one of said pair of leg plates in said state of rapid deceleration, wherein said elongated holes each have a longitudinal axis extending along a direction from said fixing portion toward said connective part.
In the webbing take-up device which is structured as described above, when the vehicle is in a state of rapid deceleration, the locking device connects the take-up shaft to at least one of the pair of leg plates so as to lock the take-up shaft. In this manner, the rotation of the take-up shaft in the pulling-out direction, which is opposite to the take-up direction, is restricted. When the vehicle is in a state of rapid deceleration, because the body of the vehicle occupant begins to move toward the front of the vehicle because of inertia, the webbing belt restraining the body of the vehicle occupant begins to be rapidly pulled out. At this time, the locking device locks the take-up shaft by connecting the take-up shaft to the leg plate and restricts the pulling-out of the webbing belt by restricting the rotation of the take-up shaft in the direction of pulling out. Thus, the force at the webbing belt for restraining the vehicle occupant is increased.
At this time, however, the excessive tensile force which pulls out the webbing belt when the body of the vehicle occupant begins to move toward the front of the vehicle due to inertia acts on the at least one leg plate that is connected to the take-up shaft by the locking device, and acts on the connecting portion via the leg plate or leg plates.
At this time, at least a portion of the tensile force acting on the connecting portion acts in a direction from the fixing portion of the connecting portion toward a connection portion of the leg plate connected to the take-up shaft via the locking device at the side connected to the take-up shaft by the locking device.
In the present webbing take-up device, the elasticity with respect to the excessive tensile force acting on the connecting portion while the vehicle is in a state of rapid deceleration is uniform because the engraved portions are formed continuously or intermittently along the direction described above, and because the intermediate portions between the engraved portions are formed such that their longitudinal directions are along the direction in which the tensile force acts and their widths are constant.
In the present invention, the direction in which the engraved portions are formed is parallel to a direction from the fixing portion toward the connection portion of the leg plate and the take-up shaft, at the side at which the leg plate is connected to the take-up shaft by the locking device. To clarify, the connection portion between the take-up shaft and the leg plate means, in a structure in which the take-up shaft and the leg plate are directly connected, the portion at which the take-up shaft and the leg plate are connected. However, if the take-up shaft and the leg plate are indirectly connected via a locking member which forms the locking device, the connection portion between the lock member and the take-up shaft is the connection portion between the take-up shaft and the leg plate. Furthermore, in the case where there is only one connection portion of the leg plate and the take-up shaft, the direction in which the engraved portions are formed is simply made parallel to the direction from the fixing portion toward the connection portion of the leg plate and the take-up shaft. In contrast, in the case where there are a plurality of connection portions and the directions from the fixing portion toward each of the connection portions are within a predetermined range of angles, the direction from the fixing portion toward the connection portion means the direction from the fixing portion toward the connection portion at which the tensile force actually acts when the tensile force acts on the leg plate. Furthermore, in the case where the tensile force acts on a plurality of connection portions, the direction from the fixing portion toward the connection portion, for the present invention, means, for example, the direction from the fixing portion toward the center of gravity of a polygon obtained by joining these connection portions.